CLASSIFICATION OF BACTERIA 53 



Genus 2. l\I('tlian<>'>i/<iax. Monotrichic short rods capable of 

 growing in the absence .of organic matter and securing growth 

 energy by the oxidation of methane (forming carbon dioxid and 

 water). Type species, Meth. methanica. 



Genus 3. Carboxydomonas. Autotrophic rod-shaped cells cap- 

 able of securing growth energy by the oxidation of carbon monoxid 

 (forming carbon dioxid). Type species, Carb. oligocarbophila 

 (Beijerinck and van Delden (1903) Orla-Jensen is described as non- 

 motile. 



Genus 4. Acetobacter. Cells rod-shaped, frequently in chains, 

 non-motile. Cells grow usually on the surface of alcoholic solutions 

 as obligate aerobes, securing growth energy by the oxidation of 

 alcohol to acetic acid. Also capable of utilizing certain other carbo- 

 naceous compounds, as sugar and acetic acid. Elongated, filament- 

 ous, club-shaped, swollen, and even-branched cells may occur as 

 involution forms. Type species, Ace. aceti. 



Genus 5. Nitrosomonas. Cells rod-shaped or spherical, motile, 

 or non-motile, if motile with polar flagella. Capable of securing 

 growth energy by the oxidation of ammonia to nitrites. Growth on 

 media containing organic substances scanty or absent. Type species, 

 Nitro. europoea Winogradsky. 



Genus 6. Nitrobacter. Cells rod-shaped, non-motile, not grow- 

 ing readily on organic media or in the presence of ammonia. Cells 

 capable of securing growth energy by the oxidation of nitrites to 

 nitrates. Type species, Nitro. Winogradskyi. 



Tribe 2.Azotobacterec5 (Nitrogen-fixing organisms). 



Genus 7. Azotobacter. Relatively large rods, or even cocci, 

 sometimes almost yeast-like in appearance, dependent primarily 

 for growth energy upon the oxidation of carbohydrates. Motile or 

 non-motile; when motile, with tuft of polar flagella. Obligate 

 aerobes usually growing in a film upon the surface of the culture 

 medium. Capable of fixing atmospheric nitrogen when grown in 

 solutions containing carbohydrates and deficient in combined nitro- 

 gen. Type species, Azotobacter chroococcum Beijerinck. 



Genus 8. Rhizobium. Minute rods, motile when young. Invo- 

 lution forms abundant and characteristic when grown under suitable 

 conditions. Obligate aerobes, capable of fixing atmospheric nitrogen 

 when grown in the presence of carbohydrates in the absence of 

 compounds of nitrogen. Produce nodules upon the roots of legu- 

 minous plants. Type species, R. leguminosarum Frank. 



FAMILY II. Pseudonwnada'cecE. Rod-shaped, short, usually 

 motile by means of polar flagella or rarely non-motile. Aerobic and 

 facultative. Frequently gelatin liquefiers and active ammonifiers. 

 No endospores. Gram stain variable though usually negative. 

 Fermentation of carbohydrates as a rule not active. Frequently 

 produces a water-soluble pigment which diffuses through the medium 



